In fixed wing aircraft, the fuel is usually stored in tanks in the main wing. A typical configuration includes a centre tank and a one or multi-compartmented main tank in each wing. The tanks are generally vented, to avoid unwanted pressurisation, and, in many configurations, it is common to have a surge tank located outboard of each main wing tank. The venting of the tanks may be through the surge tank which typically includes a NACA intake designed to maintain a modest pressurisation of the tanks when the aircraft is in flight, but to allow venting when required.
Aircraft fuel tanks are now subject to fuel tank flammability requirements (FAR25.981b). One conventional approach to meeting this requirement is to provide an “inerting system” which is effective in reducing the flammable gas within the ullage space which exists above the fuel within each fuel tank. For example, inerting systems may comprise a system in which Nitrogen Enriched Air (NEA) is generated by an On Board Inert Gas Generating System (OBIGGS) which is then pumped into the fuel tanks. This reduces the flammable oxygen content of the fuel tank. A prior art inerting system is, for example, disclosed in U.S. Pat. No. 6,585,192.
It will be appreciated that the provision of any inerting system carries a direct weight and/or space penalty for the aircraft (which may result in decreased range and/or fuel efficiency). Accordingly, there is an ongoing desire to provide alternate inerting systems.